Hollywood director James Cameron is sinking to new depths this week. As soon as stormy weather over the Pacific island of Guam clears, he will attempt to dive to the bottom of the nearby Mariana Trench in a one-man, titanium sphere he designed with Australian engineer Ron Allum.

Cameron will be filming the trench in 3D – possibly for use in the movie Avatar 2 – and he also hopes to collect sediments and a few creatures for analysis.

Submarine technology has come a long way since Piccard and Walsh did their dive. When their craft – the bathyscaphe Trieste – landed on the bottom, it inadvertently threw up a thick cloud of silt that blocked their view. Cameron's one-man submarine, Deepsea Challenger, is designed to hover just above the bottom to avoid a repeat. It will send out little rovers with cameras and snatchers.

The beauty of deep-sea diving craft, says Paul Tyler at the University of Southampton, UK, is how selective they can be. Rather than trawling to collect samples, craft such as Cameron's can reach out and grab species straight from the water.

Tyler expects it will pick up critters like sea cucumbers and squishy shrimp-like animals called amphipods."But generally, animal groups tend to decrease [in abundance] as you go down," he says. At over 1000 atmospheres of pressure – double that found on the 3000 to 6000-metre-deep abyssal plains that form most of the ocean floor – "there will be no animals with air, no fish with bladders: everything will be solid water and tissue."

Although Cameron's mission is the first crewed dive for 52 years, the Mariana Trench isn't exactly unexplored territory, says Alan Jamieson of the University of Aberdeen, UK. "Just because a human hasn't been there doesn't mean it hasn't been explored," he says. In 2009, for example, a robot submarine named Nereus made the trip, taking photos and collecting samples for researchers to sift through.

Despite the focus on the Mariana Trench, it is just one of five spots in the Pacific Ocean that are more than 10,000 metres deep. All are isolated from one another and probably contain very different organisms and geology. The Branson-backed project aims to explore these other trenches as well, and Jamieson says there is an argument to be made for even more trench exploration: "A scientific survey of Everest isn't the same as a scientific survey of Kilimanjaro."

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